As a refrigeration air conditioning hermetic compressor, there are conventional reciprocating type, rotary type and scroll type compressors, and these compressors are used in refrigeration or air conditioning fields of domestic or business purpose. Currently, compressors are developed while utilizing characteristics in terms of costs and performance.
Among them, a so-called hermetical compressor for preventing noise and eliminating the need of maintenance is a typical compressor in which a compressor mechanism and a motor are accommodated in a container, and a scroll compressor and a rotary compressor are in the mainstream. Generally, in the scroll compressor, a fixed scroll in which a scroll lap rises from a plate and an orbiting scroll are combined with each other to form a compression chamber therebetween, when the orbiting scroll is allowed to orbit in a circular orbit while restraining the orbiting scroll from rotating by a rotation-restraint mechanism, a compression chamber moves while changing its volume, thereby carrying out the suction, compression and discharge, a predetermined back pressure is applied to an outer periphery of the orbiting scroll and a back surface of a lap by lubricant oil, so that the orbiting scroll is not separated from the fixed scroll and does not flip over.
FIG. 4 shows the conventional scroll compressor (e.g., patent document 1). FIG. 4 is a sectional view of the conventional scroll compressor. Refrigerant gas sucked into the suction pipe 1 passes through the suction space 3 of the fixed scroll 2 comprising the lap 2a and the plate 2b, and is enclosed in the compression chamber 5 formed by meshing the fixed scroll 2 with the orbiting scroll 4 comprising the lap 4a and the plate 4b, the refrigerant gas is compressed while reducing the volume thereof toward the center of the fixed scroll 2, and is discharged from the discharge port 6.
A back pressure space 8a is formed such as to be surrounded by the orbiting scroll 4 and a seal ring 14 mounted in a ring-like groove of a frame 7. The pressure in the back pressure space 8a is set to an intermediate pressure between discharge pressure and suction pressure, and the intermediate pressure is controlled such that this pressure becomes constant by a back pressure adjusting mechanism 9. The seal ring 14 slides with a plate back surface 4c of the orbiting scroll 4.
The back pressure adjusting mechanism 9 has a connecting channel 10 which is in connection with a suction space 3 through the fixed scroll 2 from the back pressure space 8a, and the connecting channel 10 is provided with a valve 11. If the pressure in the back pressure space 8a becomes higher than a set pressure, the valve 11 is opened, oil in the back pressure space 8a is supplied to the suction space 3, and the pressure in the back pressure space 8a is maintained at a constant intermediate pressure. The oil supplied to the suction space 3 moves to the compression chambers 5 together with the orbiting motion, and this prevents oil from leaking between the compression chambers 5. The intermediate pressure is applied to a back surface of the orbiting scroll 4 to prevent the scroll compressor from flipping over. If the scroll compressor flips over, the fixed scroll 2 and the orbiting scroll 4 are separated, and oil leaks from that portion.
Iron-based material mainly comprising cast iron is used for the fixed scroll 2 and the orbiting scroll 4 which constitute the scroll compressor, or iron-based material is used for the fixed scroll 2 and aluminum-based material is used for the orbiting scroll 4.
(Patent Document 1)
Japanese Patent Application Laid-open No. 2001-280252
In the above structure, however, when the scroll compressor is started at a low temperature or when a large amount of liquid returns to a suction port during defrosting operation of the cycle, in order to compress liquid refrigerant, the pressure in the compression chamber 5 abnormally rises, and the orbiting scroll 4 and the fixed scroll 2 are adversely separated from each other. At that time, the plate back surface 4c of the orbiting scroll 4 abuts against a flat surface 15 of the frame 7, and there is a problem that seizing is generated.
The present invention has been accomplished to solve such a conventional problem, and it is an object of the invention to provide a reliable scroll compressor.